Three-Dimensional Printed Polymer Waveguides for Whispering Gallery Mode Sensors

Whispering gallery mode (WGM) microresonators are widely exploited for highly sensitive sensing applications due to their ultrahigh quality (Q) factor enabling single-particle detection. The WGM surface-confined resonant light recirculates around the resonator, allowing the light to interact with analytes over several round trips, which enhances the sensitivity of detection. However, the stability of efficient coupling of WGMs to ingress-egress waveguides for lab-on-chip has been problematic. The typical way to achieve WGM coupling is to use a tapered optical fiber or a prism, which makes the device either fragile or bulky, and is not conducive to sensor integration that can lead to robust lab-on-chip devices. In this letter, we demonstrate three-dimensional (3D) fabricated polymer waveguides that can be integrated and provide evanescent coupling to silica WGM microspheres without sacrificing Q factor. By mechanically connecting the waveguides to the microcavity, we can control the coupling to the resonator and the mechanical stability of the 3D lab-on-chip sensor is greatly improved. This provides a pathway to enhance the stability of WGM coupling for sensor integration.